1. Field of the Invention
The present invention relates to a power supply system and a power supply method, and particularly to a power supply system in which a semiconductor switch is provided for controlling supply of electrical power from a power supply to a load and driven in response to a drive signal, and a power supply method for controlling the supply of electrical power from a power supply to a load. More specifically, the invention relates to a power supply system and a power supply method for a vehicle.
2. Description of the Related Art
A semiconductor switch used in this type of power supply system is, for example, an n-channel MOSFET (metal oxide semiconductor field-effect transistor). Because of the extremely low on-resistance and low cost of this n-channel MOSFET, it has come to be used in automotive applications.
FIG. 7 shows such a type of power supply system in a vehicle, in which an output voltage from a 12-V power supply 101 is supplied to a load 103 via the drain D and the source S of an n-channel MOSFET 105, which is a semiconductor switch to be driven for switching.
For use to the drive, an output voltage from the 12-V power supply 101 is supplied via an ON/OFF circuit 107, where it is switched to be on and off, to a charge pump circuit 109 which is composed of a voltage stepup circuit 111 and an oscillator circuit 113. The circuit 111 steps up the supplied voltage, and a stepped-up voltage is input to the circuit 113, where it is based on to generate an oscillating raised voltage of a prescribed frequency, which is output as a control signal to the gate of the n-channel MOSFET 105, which is thereby driven to switch on and off, supplying electrical power from the 12-V power supply 101 to the load 103.
As such, in automotive applications, the n-channel MOSFET is often switched on and off at the high side (upstream of a load), where it thus has a gate-source voltage normally raised above an on-voltage, with the need for provision of a charge pump circuit.
Although the power supply system has the advantages of low cost and a low on-resistance, in applications such as use in a vehicle, it requires such extra elements as a charge pump circuit. One example of such application s in an intelligent power system (IPS) that has an n-channel MOSFET with a built-in charge pump circuit and protection circuit, and is expensive.
In addition, the charge pump circuit has an oscillator circuit, which is caused to oscillate at a high frequency (several hundreds of kilohertz) in order to achieve a reduction in size of the power supply system in vehicle. For this reason, there is an increased chance of the oscillator generating noises in the radio of vehicle. This necessitates a circuit to reduce such radio noises, thereby increasing the cost of the power supply system.
While a p-channel MOSFET can also be used on the high side, this p-channel MOSFET has a larger chip than the n-channel MOSFET, and has a higher cost than the n-channel MOSFET to achieve the same performance.
FIG. 8 shows a multiple-voltage power supply system that has not actually been used in a vehicle.
In this power supply system, a voltage (42 V) generated by an alternator 121 is charged to a 36-V battery B1 via a diode D1, and electrical power of the 36-V battery B1 is supplied to a load 123, such as a drive motor. The voltage (42 V) generated by the alternator 121 is also converted to 14 V by a DC/DC converter 125 and supplied to a 12-V battery B2, and electrical power from the 12-V battery B2 is supplied to another load 127, such as a lamp.
By use of a DC/DC converter for conversion from 42 V to 14 V, there is achieved a multiple-voltage system encompassing a battery for 36-V system and a battery for 12-V system, enabling supply of electrical power to both a high-voltage load such as a drive motor and a low-voltage load such as a lamp. The voltage of the 36-V battery is a triple of that of the 12-V battery B2, and the supply current of the former is one-third of that of the latter for the same electrical power, enabling the cross-section of conductors in wiring harness associated with the 36-V battery to be made approximately one-third of that of conductors wiring harness associated with the 12-V battery, thereby not only reducing the weight of wire harness, but also improving the load efficiency.
Accordingly, it is an object of the present invention to provide a power supply system and a power supply method that use multiple voltages permitting a simple, low-cost circuit configuration to provide easy on/off control of a load.
The present invention adopts the following configuration in order to achieve the above-noted object.
Specifically, one aspect of the present invention is a power supply system comprising a first power supply having a first supply voltage, a second power supply having a second supply voltage larger than the first supply voltage, a semiconductor switch drivable with the second supply voltage and connected between the first power supply and a load, and a drive circuit using the second supply voltage as a drive signal to drive the semiconductor switch.
According to this aspect, a multi-voltage power supply system allows a semiconductor switch to be driven with a simple, low-cost configuration, for effective supply of power to a load.
Another aspect of the present invention is a power supply system for a vehicle including a load, the power supply system, comprising a first power supply having a first supply voltage, a second power supply having a second supply voltage larger than the first supply voltage, a semiconductor switch drivable with the second supply voltage and connected between the first power supply and the load, and a drive circuit using the second supply voltage as a first drive signal to drive the semiconductor switch.
According to this aspect, in a vehicle having a load, a multi-voltage power supply system allows a semiconductor switch to be driven with a simple, low-cost configuration, for effective supply of power to the load.
Another aspect of the present invention is a power supply system for a vehicle including a motor having first and second electrodes different of polarity, and grounding circuitry, the power supply system comprising a first power supply having a first supply voltage, a second power supply having a second supply voltage larger than the first supply voltage, a first semiconductor switch connected between the first power supply and the first electrode of the motor, a second semiconductor switch connected between the first power supply and the second electrode of the motor, a third semiconductor switch drivable with the second supply voltage and connected between the second electrode of the motor and the grounding circuitry, a fourth semiconductor switch drivable with the second supply voltage and connected between the first electrode of the motor and the grounding circuitry, a first drive circuit configured to drive the first semiconductor switch, a second drive circuit configured to drive the second semiconductor switch, a third drive circuit using the second supply voltage as a drive signal to drive the third semiconductor switch, a fourth drive circuit using the second supply voltage as a drive signal to drive the fourth semiconductor switch, and a controller configured to synchronously control the first, second, third and fourth drive circuits to control a rotating direction of the motor.
According to this aspect, in a vehicle including a motor and grounding circuitry, a multi-voltage power supply system allows a set of semiconductor switches to be synchronously driven with a simple, low-cost configuration, for effective supply of power to the motor.
Another aspect of the present invention is a power supply system which performs on/off control of a semiconductor switch so as to control the supply of electrical power from a first power supply to a load. This power supply system has a second power supply with a second voltage that is larger than a first voltage of the first power supply and that can perform on/off control of the semiconductor switch, and driving means that outputs to a control input terminal of the semiconductor switch a control signal for performing on/off control of the semiconductor switch by means of the second voltage supplied from the second power supply.
According to this aspect of the present invention, when the second voltage that is larger than the first voltage of the first power supply and that is capable of on/off controlling the semiconductor switch is supplied to the control means from the second power supply, the driving means outputs to the control input of the semiconductor switch a control signal for on/off controlling the semiconductor switch by the second voltage. This results in on/off control of the semiconductor switch, and control of the supply of electrical power to the load from the first power supply. More specifically, by using the second power supply to perform on/off control of the semiconductor switch and supplying electrical power to the load from the first power supply so as to control the supply of electrical power thereto, it is extremely easy to perform on/off control of the load, without the need for a complex charge pump circuit as was used in the past, using a simple, low-cost circuit.
Another aspect of the present invention is a power supply system comprising a first semiconductor switch connected to a first power supply and to a first end of a motor, a second semiconductor switch connected to a second end of the motor and to ground, a third semiconductor switch connected to the first power supply and to the second end of the motor, a fourth semiconductor switch connected to the first end of the motor and to ground, a second power supply having a second voltage, larger than a first voltage of the first power supply and capable of on/off controlling the first and third semiconductor switches, a first driver outputting to a control input terminal of the first semiconductor switch a signal for performing on/off control of the first semiconductor switch by means of the second voltage, a second driver performing on/off control of the second semiconductor switch linked to on/off control of the first semiconductor switch, a third driver outputting to a control input terminal of the third semiconductor switch a signal for performing on/off control of the third semiconductor switch by means of the second voltage, and a fourth driver performing on/off control of the fourth semiconductor switch linked to on/off control of the third semiconductor switch.
According to this aspect, it is possible to achieve a power supply system which facilitates the forward/reverse drive of a motor, with a simple, low-cost circuit configuration, and without the need for a charge pump circuit.
Another aspect of the present invention is a power supply method comprising providing a first power supply having a first supply voltage, providing a second supply voltage larger than the first supply voltage, connecting a semiconductor switch between the first power supply and a load, the semiconductor switch being drivable with the second supply voltage, and using the second supply voltage as a drive signal to drive the semiconductor switch.
According to this aspect also, a multi-voltage power supply system allows a semiconductor switch to be driven in a simple, low-cost manner, for effective supply of power to a load.
Another aspect of the present invention is a power supply method for a vehicle including a load, the power supply method comprising providing a first power supply having a first supply voltage, providing a second supply voltage larger than the first supply voltage, connecting a semiconductor switch between the first power supply and the load, the semiconductor switch being drivable with the second supply voltage, and using the second supply voltage as a drive signal to drive the semiconductor switch.
According to this aspect also, in a vehicle having a load, a multi-voltage power supply system allows a semiconductor switch to be driven in a simple, low-cost manner, for effective supply of power to the load.
Another aspect of the present invention is a method for supplying electrical power from a first power supply to a load by performing on/off control of a semiconductor switch provided in the power supply system. This method has a step of supplying to the driving means from the second power supply a second voltage, which is larger than the first voltage from the first power supply and which is capable of on/off controlling the semiconductor switch, and a step of outputting to a control input terminal of the semiconductor switch a control signal for on/off controlling the semiconductor switch by means of the second voltage supplied to the driving means from the second power supply, thereby enabling control of the supply of electrical power from the first power supply by performing on/off control of the semiconductor switch.
That is, by using the second power supply to perform on/off control of the semiconductor switch, and also by controlling the supply of electrical power to the load by supplying electrical power thereto from the first power supply, it is extremely easy to perform on/off control of the load, without the need for a complex charge pump circuit as was used in the past, using a simple, low-cost circuit.